Ink jet printing is becoming increasingly common in recent years and ink for such use has been the subject of a great deal of research.
Crystal violet has been known for many years. Its antimicrobial properties have also been known for many years. See for example, U.S. Pat. No. 1,893,997.
The n-butyl ether of diethylene glycol has also been known for many years. It is often called Butyl Carbitol. The prior art shows the material to be antimicrobial. See, for example, U.S. Pat. No. 3,291,580. The prior art also shows the use of ethers of diethylene glycol in ink. See for example, U.S. Pat. No. 2,083,372.
U.S. Pat. No. 2,755,202 mentions crystal violet (Col. 2, line 7 and Col 6, line 46), and it also mentions lower monoalkyl ethers of diethylene glycol (Col. 5 line 15). The patent, however, contains no disclosure of the combination of these ingredients, and makes no mention whatsoever of either ink jet printing or antimicrobial activity.